1. Field of the Invention
The present invention relates to a charged particle beam irradiation apparatus and a method of irradiating an object with a charged particle beam. Further, the present invention relates to a therapeutic apparatus.
2. Discussion of Background
FIG. 10 is a block diagram showing an example of a conventional therapeutic apparatus disclosed in "Medical Physics" 1995, vol. 22, p 37 by Pedroni et al. In the conventional therapeutic apparatus, a proton beam emitted from an accelerator 1 is carried by a transporting magnet 3, and is passed through an energy degrader 5 at the first stage, as an energy attenuating means in which a predetermined amount of energy is given to the proton beam. The proton beam is bent from the horizontal direction to an upward direction by a first deflection electromagnet 11, and is returned to the horizontal direction by a second deflection electromagnet 13. Further, the proton beam is converged by a converging electromagnet 15, and swept in a vertical direction by a scanning electromagnet 17. The swept proton beam is bent by a third (the last) deflection electromagnet 19 and passes in a just downward irradiate a patient 25 through a fine-adjusting energy degrader 21 and a dose-position monitor 23. The electromagnets 11, 13, 15, 17 and 19 are integrated with the energy degrader 21 and the monitor 23 so as to constitute an irradiation gantry. The irradiation gantry rotates around the rotating axis 29, and therefore, is called as a rotating gantry.
The proton beam irradiating to the patient 25 undergoes parallel scanning in only an X direction as shown in FIG. 10 by means of the scanning electromagnet 17 and the deflection electromagnet 19. The scanning of the proton beam in an Y axial direction, which is necessary for therapy, is effected by moving an irradiation bed 27. Scanning in a depth direction (a Z direction) is obtainable by adjusting the energy of the proton beam by means of the energy degrader 21.
In the above-mentioned conventional charged particle beam irradiation apparatus, parallel beam scanning in only a uniaxial direction (the X direction in the above-mentioned example) could be obtained, and it was necessary to move in the Y direction the patient 25 along with the bed 27 during therapy. The movement of the bed 27 might be uncomfortable to the patient, and at the same time, there may be an error of position in an irradiate area. Further, in the conventional apparatus, it was necessary to dispose the scanning electromagnet 17 at an upstream side of the deflection electromagnet 19 so as to obtain parallel beam scanning. Accordingly, the size of the deflection electromagnet 19 for deflecting the charged particle beam scanned by the scanning electromagnet 17 in the vertical direction, was increased, with the result that the total weight of the rotating gantry used for therapy was 100 tons or more. Further, the conventional apparatus had a problem with respect to the scanning in the depth direction with use of the energy degrader 21. Namely, the thickness of the energy degrader 21 was determined for each depth of scanning in a discontinuous manner, and beam irradiation was conducted in accordance with a predetermined distribution of irradiated particle number and depth so that a uniform dose of absorbed beam could irradiate a tumor. Accordingly, there was an influence of a shift of position in the irradiation area due to the breathing of the patient.